One of the problems known to be associated with vacuum cleaners is that of noise. It is also perceived that a vacuum cleaner having a higher measure of “airwatts” (which is related to the amount of suction developed by the cleaner at the inlet thereof) will perform better than a vacuum cleaner having a lower measure of airwatts. In relation to the latter, it is well understood that minimising friction losses and pressure drops within the cleaner will result in a maximised measure of airwatts.
In general, the outlets of cyclonic separating apparatus are normally formed by cylindrical tubes, also known as vortex finders. The prior art shows that it is known to recover pressure in cyclonic separating apparatus by providing symmetrical arrangements of blades or vanes in the outlets thereof such that the spiralling airflow is straightened. See, for example, U.S. Pat. No. 2,771,157. The blades or vanes are commonly shaped so that the upstream end is curved into a generally helical shape. However, these arrangements do not address the problem of noise in vacuum cleaners and other apparatus.
It is an object of the invention to provide cyclonic separating apparatus which, when in use, is comparatively quiet and also, when used in a vacuum cleaner, provides the vacuum cleaner with a comparatively high measure of airwatts. It is a further object of the invention to provide a simplified and economical way of achieving these improvements.
The invention provides cyclonic separating apparatus having a separating chamber, an inlet communicating with the separating chamber and an outlet, the outlet being formed by a conduit communicating with the interior of the separating chamber and having a longitudinal axis, wherein a single, planar baffle projects radially inwardly from an interior surface of the conduit towards the longitudinal axis.
The provision of a single baffle within the conduit has been shown to reduce the pressure drop across the cyclone separator in comparison to a cyclone separator without such a baffle. The baffle is simple and easy to manufacture integrally with the vortex finder if desired.
The reasons why the observed benefits, particularly in relation to noise, are achieved by the provision of the baffle are not fully understood. It is thought possible that the presence of the baffle may interfere with the precession of internal vortices around the conduit as the airflow passes out of the apparatus, thus reducing the amount of noise generated by these vortices. However, it may transpire that other explanations will be discovered at a later date.
Preferably, the baffle projects across at least one quarter, more preferably across substantially one third, of the diameter of the conduit. It is preferred that the baffle extends along at least one quarter of the length of the conduit, more preferably along at least half of the length of the conduit and still more preferably along substantially the entire length of the conduit. Testing has shown that these arrangements produce good results.
In a preferred embodiment, the upstream end of the baffle lies adjacent the upstream end of the conduit. This is because the effectiveness of the baffle in relation to noise reduction is greatest if the baffle lies towards the upstream end of the conduit.
The upstream and downstream ends of the baffle are also preferably curved or tapered so that the risk of fluff or threads being caught on the baffle is minimised.
In a further preferred embodiment, the baffle is provided in combination with at least one longitudinally-extending groove formed in the interior surface of the conduit. This combination maximises the noise reduction achievable.